This invention relates to a method of collecting and processing spectral data obtained from the detection of electromagnetic radiation reflected from the earth's surface.
The invention is particularly suitable for indicating areas in which hydrocarbon seepage from buried oil or gas reservoirs is occurring. Such seepage causes visible changes in the reflectance spectra of the earth's surface. One prior method utilizes LANDSAT satellite spectral data to assist in identifying areas of hydrocarbon seepage, wherein a section of the earth's surface is first selected, the section being divided into a plurality of subsections or pixels. A brightness or intensity value is obtained in LANDSAT band 4 (500 nm-600 nm wavelength range) for electromagnetic radiation reflected from each pixel, and a similar procedure is carried out for each pixel in respect to LANDSAT band 5 (600 nm-700 nm wavelength range). A cumulative probability density function value is then calculated for each pixel's corresponding band 4 and 5 brightness values. The two cumulative probability density function values obtained for each pixel are then utilized to obtain a ratio. This ratio is most conveniently derived by dividing the cumulative probability density for band 5 into the cumulative probability density for band 4. Pixels are identified as having hydrocarbon seepage if those pixels have associated ratios above a predetermined value. Although this method serves to predict areas of hydrocarbon seepage somewhat effectively, it would be desirable to improve on the results obtained by this method.